A substantial proportion of developmentally disabled children engage in self-injurious behavior (SIB) severe enough to permanently affect their health and development. While various behavioral procedures have been demonstrated to be effective in reducing this serious disorder, systematic research has not been conducted on the conditions which result in differential rates of SIB, its cause, or the best method of remediation. An experimental methodology that clearly identifies differential responding across stimulus settings can represent a key contribution in that: (a) such differential responding strongly suggests environmental influences on the behavior; (b) hypotheses can begin to be formulated and tested about the differing contingencies functioning in these environments; and (c) such a methodology can serve as a basis for testing the effects of both behavioral and biological interventions on high and low rates of responding. Our research over the past four years has resulted in a method for empirically assessing differential rates of SIB across stimulus settings which are analogues of children's normal, daily living situations. We now propose to conduct studies, formalizing this experimental methodology and demonstrating its diagnostic utility in selecting the most effective treatment procedure(s). Specifically, Study I will measure SIB across environmental assessment variables of (1) high and low demand characteristics, (2) contingent, non-contingent and no social attention, and (3) the presence and absence of age-appropriate stimulation. Study II will evaluate the effectiveness of treatment procedures selected on the basis of environmental assessment. Study III will compare the effectiveness of treatment procedures based on environmental assessment, with alternative procedures already documented successful in previous research. Together with already ongoing pilot studies, this research will serve as the basis for continuing bio-behavioral investigations on the etiology and treatment of self-injury.